Method for improving the sweep of underground reservoirs by exploiting individual reservoir segments

ABSTRACT

The sweep of an underground hydrocarbon formation having reservoir segments with trapped fluids therein is increased by locating wells in individual segments and producing simultaneously therefrom, while under the influence of an active aquifer, either native or by flooding.

United States Patent Inventor Anthony F. Altamira Houston, Tex. Appl. No. 786,567 Filed Nov. 24, 1968 Patented June 8, 1971 Assignee Texaco Inc.

New York, N.Y.

METHOD FOR IMPROVING THE SWEEP 0F UNDERGROUND RESERVOIRS BY EXPLOITING INDIVIDUAL RESERVOIR SEGMENTS 7 Claims, 6 Drawing Figs.

US. Cl 166/245, 166/263 Int. Cl ..E21b 43/16, 1521b 43/20 [50] Field of Search 166/245, 263, 268, 273-275 [56.] References Cited OTHER REFERENCES Muskat, Physical principles of Oil Production, First Edition, McGraw-Hill Book Company, lnc., New York, (1949), (pages 645 to 650 and 816 to 820 relied on.). TN871M8.

Primary Examiner-Stephen J. Novosad Attorneys-K. E. Kavahagh and Thomas H. Whaley ABSTRACT: The sweep of an underground hydrocarbon formation having reservoir segments with trapped fluids therein is increased by locating wells in individual segments and producing simultaneously therefrom, while under the influence of an active aquifer, either native or by flooding.

PATENTED JUN 8 MI METHOD FOR IMPROVING THE SWEEP OF UNDERGROUND RESERVOIRS BY EXI'LOI'TING INDIVIDUAL RESERVOIR SEGMENTS FIELD or THE INVENTION This invention relates generally to the production of hydrocarbons from underground hydrocarbon-bearing formations, and more particularly, to a method for increasing the sweep of hydrocarbons therefrom.

BACKGROUND OF THE INVENTION In the production of hydrocarbonsfrom permeable un-, derground hydrocarbon-bearin g formations, it is customary to drill one or more boreholes or wells into the hydrocarbonbearing formation and produce hydrocarbons, such as oil, through designated production wells, either by the natural formation pressure or by pumping the wells. Sooner or later, the flow of hydrocarbons diminishes and/or ceeses, even though substantial quantities of hydrocarbons are still present in the underground formations.

Frequently, many hydrocarbon-bearing formations are di? vided into reservoir segments, each containing traps wherein hydrocarbons have accumulated. These segments in the underground reservoir may be caused by faulting, permeability pinch outs, tar barriers and the like.

SUMMARY OF THE INVENTION It is an overall object of the invention to provide an im: proved recovery procedure to obtain maximum sweep of a segmented reservoir involving a plurality of wells located strategically, viz by having at least one production well in communication with each individual reservoir segment, being under the influence of an active aquifer.

It is desirable that production be initiated and continued from wells on both sides of the sealing fault dividing the for: mation into reservoir segments, when such is known to exist, until breakthrough occurs at either or both. at which time further production is discontinued and the well or wells shut in. In the absence of a native aquifer, a water drive may be substituted.

Other objects, advantages and features of this invention will become apparent from a consideration of the specification with reference to the FIGS. in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. Ia illustrates the sweep and breakthrough when the production well in communication with a reservoir segment defined by a fault is on the same side of the fault as the injec: tion well.

FIG. lb illustrates the pressure distribution of the reservoir in the situation as disclosed in FIG. la;

FIG. 2a illustrates the areal sweep obtained when the production well exploited a reservoir segment defined by a sealing fault is located behind the fault away from the injection well;

FIG. 2b illustrates the areal sweep. when an additional production well is placed in operation on the near side of the fault with respect to the injection well as a modification of FIG. 2a; I

FIG. 3a illustrates the areal sweep when the production wells on either side of a fault are produced concurrently till individual breakthrough; and

FIG. 3b discloses the pressure distribution corresponding to. the areal sweep in FIG. 3a, indicating a better sweep.

The objects of the invention are achieved by the use of an injection well in combination with production wells which are separated from each other by a sealing fault and have more or. less direct communication with the injection well.

The specification and the FIGS. of the drawings schemati: cally disclose and illustrate the practice and the advantages of the invention with well arrangements and areal sweep examples which have been observed in potentiometric model stu-,

dies which simulate recovery operations. A rectangular model of uniform thickness was used to simulate a reservoir bounded by faults from sides, i.e. a fault block, with the reservoir having two equal segments caused by a sealing fault. The model studies indicate a sweep obtained in an ideal reservoir, although the recovery by an actual sweep of a particular field may be greater or less, depending on field parameters.

" The results to be described were based on the following set of experimental conditions and assumptions:

1. The ratio of total fluid production rates between wells is constant for any given phase or step in the production plan.

.1. The total amount of fluid injected is equal to the amount of fluid produced.

3. The mobility ratio of the displacing to displaced fluid is 4. The permeability and thickness of the formation is uniform.

5. Gravitational effects are not considered.

Throughout the FIGS. of the drawings, the same symbols will be maintained as follows:

The solid circle indicate a production well, the crossed circle indicates a shut in well, an open circle a well site, and an arrowed open circle indicates an injection well, 1

Referring to FIG. 10, there is illustrated the sweep obtaine by model study when the well at x is produced to breakthrough, this production well being on the same side of the sealing fault as the injection well for the extraneous driving fluid at A. The sweep area amounts to 56.5 percent.

In FIG. 1b, there is illustrated the pressure distribution of a reservoir model, when the reservoir is exploited as in FIG. la. The poor pressure distribution above the sealing fault is quite evident and is explanatory of the low sweep percentage.

FIG. 2a illustrates the sweep obtained in the model used in FIG. Ia when production is initiated and maintained at y, located above the sealing fault, until breakthrough, resulting in a swept area of 66.2 percent.

In FIG. 2b, the sweep has beeriraised to 81.6 percent, after well y is shut in after breakthrough, by maintaining production at well x located on the near side of the sealing fault until breakthrough thereat.

In FIG. 31;, there is illustrated the sweep in the same reservoir model as in FIG. Ia when both production wells x and y, located on opposite sides of the sealing fault are produced concurrently at equal rate with the injection well at A, until the driving fluid breaks through at well x. The interface at the end of this first phase is shown as a dotted line in the upper portion of the reservoir model. In the second phase, production well t is shown as shut in, and well y is produced until breakthrough of the injection fluid. The final sweep is increased to .3 percent. The great increase in sweep over that illustrated in FIGS. 1a and his attributable to the fact that there is an additional sweep on both sides of the sealing fault due to the pressure distribution resulting from the concurrent production from wellsx and y.

FIG. 3b illustrates the pressure distribution in the reservoir model when the reservoir is to be exploited as in FIG. 3a.

Throughout the experiments, the flow of fluid through a reservoir system is governed by Darcys Law and is assumed to be sufficiently slow for the inertia forces to be negligible (i.e. Stokes flow, with low Reynolds number), and therefore is in the direction toward decreasing pressure and proportional to the pressure gradient.

The advantages of the method disclosed above are evident. More reservoir fluids are recovered prior to. breakthrough of injection fluid, and so more ultimate recovery is obtained as compared with other production methods.

Although this disclosure has illustrated the practice of this invention as directed to a secondary recovery operation, particularly employing driving displacement fluid, the advantages obtainable in the practice of this invention may be realized in primary hydrocarbon production wherein the location of the sealing fault is known in order that additional production wells may be employed.

Other modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

lclaim:

l. A method of producing formation fluids including hydrocarbons from an underground hydrocarbonbearing formation having divided reservoir segments containing trapped fluids therein which comprises penetrating said formation with at least three wells, an injection well and a pair of offset production wells in communication with individual segments, injecting an extraneous fluid into said formation having said segments via said injection well to displace said fluids including hydrocarbons in said formation toward said production wells, initiating producing said fluids including hydrocarbons from said formation via said production wells and maintaining the same concurrently until said extraneous fluid is produced along with said formation fluids at a production well, thereupon shutting in the last mentioned production well while continuing producing said fluids including hydrocarbons from said formation via the other production well while maintaining injecting said extraneous fluid into said formation via said injection well.

2. In the method of producing formation fluids including hydrocarbons as defined in claim 1, said other production well being shut in upon breakthrough of said extraneous fluid thereat.

3. In the method of producing formation fluids including hydrocarbons as defined in claim I, said production wells being located on opposite sides of a sealing fault in a reservoir segment and having more or less direct communication with said injection well.

4. in the method of producing formation fluids including hydrocarbons as defined in claim 1, continuing producing formation fluids via the production well after breakthrough of said extraneous fluid thereat while simultaneously producing formation fluids from the other of said production wells until breakthrough of said extraneous fluid thereat.

5. in the method of producing hydrocarbons as defined in claim 1, producing formation fluids via said production wells until all the production therefrom comprises said extraneous fluid.

6. In the method of producing formation fluids including hydrocarbons as defined in claim 1, said extraneous fluid being an aqueous fluid.

7. In the method of producing formation fluids including hydrocarbons as defined in claim 1, said extraneous fluid being a gas. 

2. In the method of producing formation fluids including hydrocarbons as defined in claim 1, said other production well being shut in upon breakthrough of said extraneous fluid thereat.
 3. In the method of producing formation fluids including hydrocarbons as defined in claim 1, said production wells being located on opposite sides of a sealing fault in a reservoir segment and having more or less direct communication with said injection well.
 4. In the method of producing formation fluids including hydrocarbons as defined in claim 1, continuing producing formation fluids via the production well after breakthrough of said extraneous fluid thereat while simultaneously producing formation fluids from the other of said production wells until breakthrough of said extraneous fluid thereat.
 5. In the method of producing hydrocarbons as defined in claim 1, producing formation fluids via said production wells until all the production therefrom comprises said extraneous fluid.
 6. In the method of producing formation fluids including hydrocarbons as defined in claim 1, said extraneous fluid being an aqueous fluid.
 7. In the method of producing formation fluids including hydrocarbons as defined in claim 1, said extraneous fluid being a gas. 